1. Field of the Invention
The present invention relates to a portable wireless communication apparatus, and more particularly, to a portable wireless communication apparatus having an antenna being capable of attaining a broadband antenna characteristic with a simple structure.
2. Description of the Related Art
In general, to incorporate an antenna in a folding mobile phone, for instance, a number of measures have been taken to meet form-factor reductions of the mobile phone and/or attain an increased antenna characteristic so that each circuit part incorporated in the mobile phone has no effect on the antenna characteristic (See Patent Documents 1, 2 and 3, for instance).
A folding mobile phone as disclosed in the Patent Documents 1 has two casings, and components required for the mobile phone are all housed in one casing. The other casing is covered with a conductive film having a window. The folding mobile phone is configured so that the above conductive film and a substrate in the casing with the components housed are respectively used as an antenna element and a ground conductor to configure a mono-pole antenna when the mobile phone is unfolded, or to operate as a patch antenna when the mobile phone is folded over.
A portable wireless communication apparatus as disclosed in the Patent Document 2 is that having an antenna mounted to a casing bend part. The portable wireless communication apparatus is configured so that a connection cable extending over both two casings has at an intermediate portion a resistance and/or an inductor to ensure that cutoff of upper and lower circuits respectively incorporated in the two casings is achieved in a high-frequency bandwidth.
A mobile phone as disclosed in the Patent Document 3 has two casings, and one casing incorporates a plate-shaped element operating as an antenna. The other casing incorporates a transmission/reception circuit that is connected to the above element through a feeder. The mobile phone is configured so that the plate-shaped element has a plurality of holes for mounting components in an embedded state to ensure that components or the like on a circuit substrate have no effect on the plate-shaped element and that the plate-shaped element operates as a mono-pole antenna when the mobile phone is unfolded.
[Patent Document 1]
    Japanese Patent Laid-open No. 2000-216611 (Page 3 and FIGS. 1 to 3)[Patent Document 2]    Japanese Patent Laid-open No. Hei 9-270728 (Page 2 and FIGS. 3 and 4)[Patent Document 3]    Japanese Patent Laid-open No. 2001-156898 (Pages 4 and 5 and FIG. 1)
In the folding mobile phone as disclosed in the Patent Document 1, the conductive film and the substrate in the casing with the components housed need to be cut off in a high frequency bandwidth to allow the conductive film and the substrate to operate as the mono-pole antenna.
However, when upper and lower substrates are connected together through a printed circuit board, the conductive film and the printed circuit board result in the same potential state. Thus, the folding mobile phone has a difficulty in attaining an increased antenna characteristic.
The portable wireless communication apparatus as disclosed in the above Patent Document 2 is cited as one of approaches to solving the above problems. However, this portable wireless communication apparatus is limited in cutoff-enable frequency bandwidth depending on the kind of components such as the resistance and the inductor. Thus, a system requiring a broadband frequency bandwidth is hard to effect cutoff in the whole frequency bandwidth. In addition, the above portable wireless communication apparatus has the disadvantage of causing delays in a transmission characteristic (time constant of a pulse signal) of a signal such as a control signal transmitted over the connection cable.
The mobile phone as disclosed in the above Patent Literature 3 is also cited as one of approaches to solving the above problems. However, in this portable phone, when the above components include those contributing to short-circuiting of ground faces of both the substrates through the connection cable, the antenna characteristic is sometimes degraded unless a sufficient distance from a plate-shaped antenna is kept.
Also, when this mobile phone has a larger hole in the conductive film considering a wavelength, the presence of this larger hole causes current mode variations (in other words, this larger hole operates as a slot antenna or a notch antenna), and thereby has an effect on the antenna characteristic. Further, it is feared that the above mobile phone causes capacitive coupling or short-circuiting between signal lines in the connection cable and the plate-shaped antenna depending on an available frequency bandwidth so that a high frequency current induced on the plate-shaped antenna conducts over the signal lines to exert an adverse effect on a wireless circuit. The above mobile phone also causes a thermal loss of the high frequency current depending on a terminal load of the signal lines, and this heat loss of the high frequency current is attributable to remarkable degradation of the antenna characteristic.